The proposed work covers two areas. In the first, phosphorus analogs of nitrogen compounds used in the chemotherapy of cancer and leukemia are being prepared for study of their chemistry and possible activity. The compounds under study include phosphorus mustards and small-ring heterocycles containing phosphorus, including phosphirans (three-membered CCP rings) and phosphetans (four-membered CCCP rings). The second area involves the preliminary study of methods for the preparation of macrocyclic systems containing phosphorus donor sites. These compounds may be expected to show cation selectivity in their coordinating properties and may in consequence, like the cyclodepsipeptide antibiotics, show biological activity. Methods under investigation include template cyclisations involving both complexes of phosphorus donors, and complexes of non-phosphorus donors.